Y1-D300-AC-14-357 

February 12, 2015 

Docket Management Facility 

U.S. Department of Transportation 

1200 New Jersey Avenue, S.E. 

West Building Ground Floor 

Room W12-140 

Washington, DC 20590 

The Boeing Company 

6001 S. Air Depot 

Oklahoma City, OK 73135 

Subject: Petition for Exemption from Title 14 Code of Federal Regulations (CFR) §25.345(c) in 

Support of FAA Project ST00279MC-T (ODA Project 192) for the Model767-2C 

The Boeing Company respectfully submits the enclosed Petition for Exemption from Title 14 Code of Federal 

Regulations (CFR) §25.345(c) Arndt. 25-91 from the Certification Basis for FAA Project ST00279MC-T (ODA 

Project 192) for the Model 767-2C. 

The enclosure provides the details of the petition in accordance with 14 CFR § 11.81. 

DESCRIPTION OF RELIEF SOUGHT: USAF requires that the KC-46A be capable of refueling all aircraft that 

may currently be refueled using KC-135 and/or KC-10A tankers. Some of these receiver aircraft refuel at low 

speeds that would require prolonged flight with high lift devices deployed during aerial refueling operations. 

Application of 14 CFR §25.345(c) would drive increased maneuver and gust loads resulting in impractical 

redesign of the wing structure. The airplane design provides adequate structural capability for aerial refueling 

operations with high lift devices deployed due to the limited maneuvering and the low frequency of occurrence. 

The petitioner requests an exemption from 14 CFR §25.345(c). 

As stated in 14 CFR § 11.87, the petitioner requests that this Petition for Exemption not be delayed by the public 

process, which includes publication of the subject petition. If this exemption is not granted, it could lead to 

delays in the delivery of the STC modified 767 -2C to the USAF at a critical time of need. The STC modified 

767-2C approved aircraft will not be eligible to receive a civil airworthiness approval or standard certificate of 

airworthiness. It is intended that the aircraft will be maintained as a public use aircraft only for the life of the 

product. 

Granting of this exemption petition is kindly requested by July 15, 2015. 

If you have any questions, please do not hesitate to contact the undersigned. 

Sincerely, IJ_ Q _ tJ ~"~~~ T11l10thY P. Wehman .;,('QIV ~~rHo~ JR Brownell 

ODA-501296-CE Certification Engineer ODA-501296-CE Administrator 

Phone: 405-582-8908 Phone: 425-266-4539 

Mail Code: R7-53 Mail Code: R7-53 

Enclosure: Petition for Exemption from Title 14 Code of Federal Regulations · 

§25.345(c) Arndt. 25-91 

cc: Joel Ligon (FAA Wichita MCO Program Manager) 

James Hartley (FAA Wichita ACO OMT Lead) 

Jeff Duven (FAA Transport Airplane Directorate Manager) 
Enclosure to Yl-D300-AC-14-357 

Page I of6 

Petition for Exemption from Title 14 Code of Federal Regulations§ 25.345(c) Arndt 25-91 

Name and Address of the Petitioner 

David Horn, ODA Lead Administrator 

The Boeing Company 

6001 S. Air Depot, M/S R7-53 

Oklahoma City, OK 73135 

Section(s) of the Regulations from which Relief is sought: 

14 CFR §25.345(c) High lift devices 

(c) If flaps or other high lift devices are to be used in en route conditions, and with flaps in the appropriate 

position at speeds up the flap design speed chosen for these conditions, the airplane is assumed to be 

subjected to symmetrical maneuvers and gusts within the range determined by--

( 1) Maneuvering to a positive limit load factor as prescribed in Sec. 25.337(b); and 

(2) The discrete vertical gust criteria in Sec. 25.341 (a). 

The Extent of Relief Sou ht and Reason(s) 

Regulation Requires: Relief is Necessary because: 

14 CFR § 25.345 (c) Flap usage in en route conditions Applying this requirement to the use of high 

Amendment 25-91 must be considered at the positive lift devices during aerial refueling operations 

maneuvering requirements of 14 would drive increased maneuver and gust 

CFR 25.337(b) and symmetric loads resulting in impractical redesign of the 

gust requirements of 14 CFR wing and leading and trailing edge structures. 

25.34l(a). 

Description of Issue 

USAF requires that the KC-46A be capable of refueling all aircraft that may currently be refueled using KC135 and/or KC-IOA tankers. Some ofthese receiver aircraft refuel at low speeds that would require 

prolonged flight with high lift devices deployed during aerial refueling operations. The intent of the 

requirement of 14 CFR §25.345(c) may be satisfied by consideration of the expected usage of the KC-46A 

airplane, operational procedures, and inherent structural capability. 

Note that the KC-lOA requires a similar low speed refueling envelope with flaps down operation. The current 

en route flaps requirements of 14 CFR §25.345(c) were not part ofthe KC-IOA certification basis. 

Expected Usage 

Low speed refueling should be regarded as a customer required capability and not as common usage as 

envisioned by the regulation. This capability is expected to be utilized very infrequently as these flaps down 

refueling events are not part of the KC-X specification mission profiles which form the basis for structural 

durability evaluation. For any KC-46A, the frequency of low altitude refueling missions, including flaps 

down refueling, is expected to be less than I 0 hours/year, equivalent to I o-2 per flight hour. 
Enclosure to Yl-0300-AC-14-357 

Page 2 of6 

Petition for Exemption from Title 14 Code of Federal Regulations§ 25.345(c) Arndt 25-91 

Flaps down refueling operations are low speed, in the range of 185 to 200 KIAS and below the flaps down 

maximum altitude limit of20,000 ft. Flaps will not be deployed during high speed or high altitude flight. 

Only takeoff flap settings, detents 1, 5, 15, and 20, may be used. Since flaps 1 and 5 are sufficient to perform 

these missions, flaps 15 and 20 usage is expected to be rare. 

This operation is expected to be very infrequent. Therefore, the cumulative lifetime refueling flaps down 

operation is not significant both from an exposure to elevated maneuver and gust environment and effects on 

the overall structural durability. 

Operational Procedures 

For aerial refueling operations, turbulence is avoided and the fuel offload maneuvering limit is 1.5g's. Similar 

to the KC-1 OA aerial refueling operations manual, AFI 11-2KC-l 0 V3, the KC-46A operations manual will 

instruct the flight crew to terminate refueling if moderate turbulence is encountered. 

Situational awareness is high due to proximity of receiver aircraft. When not in preparation or execution of 

slow receiver offload, the tanker aircraft would operate flaps up to minimize fuel burn during loiter segments. 

When not oftloading, flaps down maneuver limits remain at the current AFM limit, Og to 2g. 

Structural Capability 

As discussed in the Amendment 25-46 publication preamble, the current requirement for consideration of en 

route flaps is intended to address situations where the airplanes are "commonly flown in en route conditions 

with flaps deployed for purposes other than as speed brakes, and the airplane structure should be designed for 

the appropriate loads regardless of the operational reason". Sufficient and appropriate structural capability for 

the expected flaps down refueling operations is provided by the existing design both for offload operations 

and for loading conditions following disconnect. 

In the event that severe turbulence is encountered during aerial refueling operations, the KC-46A structural 

capability is sufficient for the effects of the gust and rapid refueling termination and disconnect. Rapid 

disconnects and resulting fuel pressure transients are addressed in the basic USAF approved aerial refueling 

criteria. In the event of a rapid disconnect followed by high maneuvering or severe gusts, the aircraft loads are 

limited by airplane lift capability to the existing structural capability as described below. 

During operation in the low speed refueling regime, the vertical maneuvering and gust loads are naturally 

limited by airplane maximum lift capability to envelopes comparable to the flaps down envelope required by 

14 CFR §25.345(a). Encounters with severe head on gusts, while not required by 14 CFR 25.345(c), are also 

very unlikely to exceed structural capability during these operations. 

Since flaps 1 and 5 are expected to be used most often, the maneuvering and gust capabilities are shown for 

flaps 5, the most critical. Flaps 15 and 20 are available, but refueling operations with these settings is 

expected to be rare and are not considered. 
Enclosure toY 1-0300-AC-14-357 

Page 3 of6 

Petition for Exemption from Title 14 Code of Federal Regulations§ 25.345(c) Arndt 25-91 

Figure 1 shows the maximum lift limited maneuvering capability on a speed-load factor plot at maximum 

gross weight for flaps 5 operation. This figure illustrates that the positive maneuvering and vertical gust loads 

would not be severe and also illustrates that high weight operations are not practical because of reduced 

maneuvering margins to stick shaker. For flaps 1, the maximum lift capability is even lower and the same 

conclusions 

... 

-.. 

6 

t1 

.! 

3.00 

2.50 

11 1.50 

~ 

0 

Maneuvering and Gust Capability 

Weight = 4l5,00Q Lbs 

CG =23~ 

lO,OOQft. 

Flaps 5 

--- ---

Gust Envelope 

_per 15.341 

(Pratt Formula) 

-~-

100 

C-130 

150 200 

Speed· KEAS 

Positive Maneu~ring 

Envelope per 25.337 

/ I J , 

/ , 

, " 

---

150 

VF 

Figure 1- Maneuver and Gust Capability at 415,000 Lbs.- Maximum Weight Case 

Figure 2 shows the same envelope at a more likely weight for this mission. Once again, the maneuver and 

gust capability is adequately covered by the flaps down maneuvering capabilities. The structural capability is 

quite adequate for performing these low speed refueling missions. For operations at lower weights, 

exceedance of the flaps down maneuver envelope would not exceed stmctural capability. 
Enclosure to Yl-D300-AC-14-357 

Page 4 of6 

Petition for Exemption from Title 14 Code of Federal Regulations§ 25.345(c) Arndt 25-91 

2.00 

·oo "' 

.: 

0 

t 

{1, 

"0 1.50 "' 0 

.... 

3 

'f 

~ 1.00 

0.50 

0 50 

Maneuvering and Gust Capability 

ManeiJveriflg Enve ope 

per25.3~7 

1-----· ---t-----.....J-.----h··--l-~+--------·-1 'I ~ , 

, 

Vf 

------

100 150 200 250 300 

Speed· KEAS 

Figure 2- Maneuver and Gust Capability at 350,000 Lbs.- Expected Typical Heavy Operations Case 

A head on gust resulting in an over speed of flap capability would be extremely improbable. For the worst 

case scenario, 200 knot refueling condition at flaps 5, a head on gust intensity of 1 I 6 feet per second, EAS, 

would be needed to exceed the VF+I5 speed, 269 KEAS, for the 14 CFR §25.345(b) head on gust design 

condition. Gust levels of these magnitudes are extremely rare events in normal level flight. For comparison, 

the 10,000 ft. altitude design vertical gust per 14 CFR §25.341 is about 50 feet per second, EAS. For flaps 1, 

the gust margin is even larger, 137 feet per second, EAS. This further illustrates the adequacy ofthe existing 

structural design. 

Statement of Public Interest 

USAF requires that the KC-46A be capable of refueling all aircraft that may currently be refueled using KC135 and/or KC-1 OA tankers. Some of these receiver aircraft refuel at low speeds that would require prolonged 

flight with high lift devices deployed during aerial refueling operations. Application of 14 CFR §25.345(c) 

would cause significant modification to the airplane that would provide no net benefit in the configuration and 

no commensurate increase in safety. If the relief is not granted, it could lead to delays in the delivery of the 
Enc.losure to YI-D300-AC-14-357 

Page 5 of6 

Petition for Exemption from Title 14 Code of Federal Regulations§ 25.345(c) Arndt 25-91 

STC modified767-2C to the USAF at a critical time of need. It remains in the public's interest to grant Boeing 

an exemption to 14 CFR §25.345(c) for the STC modified 767-2C airplane. 

Statement of No Adverse Effect on Safety 

The basic flaps down design capability provides adequate structural capability for flaps down refueling 

operations consistent with the intent of the rule. Application of the specific 14 CFR §25.345(c) en route 

requirements is not appropriate as the low speed capability requirement does not represent typical tanker 

usage and the operational procedures will ensure that the KC-46A airplane is operated in a manner to avoid 

structural overload. 

Since these low speed aerial refueling operations are expected to be infrequent and well below the common 

usage intended per 14 CFR §25.345(c) en route requirements, these operations are not equivalent to the en 

route flaps usage as envisioned by the pertinent regulations. An exemption is requested based upon the 

appropriate compensating factors considering the expected usage of the airplane, basic structural capability, 

and operational procedures. 

Request to Waive Publication and Comment 

As allowed in 14 CFR § 11.87, the petitioner requests that this Petition for Exemption not be delayed by the 

public process, which includes publication of the subject petition. If this exemption is not granted, it could 

lead to delays in the delivery of the STC modified 767-2C to the USAF at a critical time of need. The STC 

modified 767-2C approved aircraft will not be eligible to receive a civil airworthiness approval or standard 

certificate of airworthiness. It is intended that the aircraft will be maintained as a public use aircraft only for 

the life of the product. 

Privileges ofthe Exemption Outside the United States 

Not requested 

Conclusion 

The Boeing position is that for aerial refueling operations involving flaps down usage, the expected usage, 

operational procedures and structural capability provides justification for an exemption to 14 CFR §25.345(c) 

based on the limited maneuvering and the low frequency of occurrence of flaps down refueling operations. 

Boeing herby requests FAA issuance of an exemption for 14 CFR §25.345(c) Arndt 25-91, based on the 

rationale presented above, for the FAA Project No. STC00279MC-T- Model 767-2C. 

Summary to be Published in the Federal Register 

PETITIONER: The Boeing Company 

SECTION OF 14 CFR AFFECTED: 14 CFR §25.345(c) 
Enclosure to YI-D300-AC-14-357 

Page 6 of6 

Petition for Exemption from Title 14 Code of Federal Regulations§ 25.345(c) Arndt 25-91 

DESCRIPTION OF RELIEF SOUGHT: USAF requires that the KC-46A be capable of refueling all aircraft 

that may currently be refueled using KC-135 and/or KC-1 OA tankers. Some of these receiver aircraft refuel at 

low speeds that would require prolonged flight with high lift devices deployed during aerial refueling 

operations. Application of 14 CFR §25.345(c) would drive increased maneuver and gust loads resulting in 

impractical redesign of the wing structure. The airplane design provides adequate structural capability for 

aerial refueling operations with high lift devices deployed due to the limited maneuvering and the low 

frequency of occurrence. The petitioner requests an exemption from 14 CFR §25.345( c).